Alaska Fishery Research Bulletin Issues, Vol.5 No. 2 - Winter 1998

Experimental Effects of Soak Time on Catch of Legal-Sized and Nonlegal Red King Crabs by Commercial King Crab Pots

Douglas Pengilly and Donn Tracy - Vol. 5(2):81-97. 1998.

An experiment was conducted in Bristol Bay, Alaska, to assess the effects of soak time on catch per pot of legal (males greater than or equal to 165 mm carapace width) and nonlegal (females and sublegal-sized males) red king crabs Paralithodes camtschaticus. Soak times of 12, 24, and 72 h were tested because they cover the typical range of soak times in the Bristol Bay commercial fishery. Catch per pot increased with each increase of soak time for both legal and nonlegal red king crabs, but catch per pot per soak-hour decreased with increasing soak time. Additionally, the ratio of nonlegal red king crabs to legal red king crabs decreased with increased soak time, although local conditions were also shown to have a significant effect on bycatch rates of nonlegal crabs.

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A Simple Stratified Design for Mark-Recapture Estimation of Salmon Smolt Abundance

Stan R. Carlson, Lewis G. Coggins Jr., and Charles O. Swanton - Vol. 5(2):88-102. 1998.

We describe a mark-recapture (M-R) technique in which a stratified design and sampling at 1 or 2 stream locations are used to estimate the abundance of a migrating salmon smolt population. The method consists of counting smolts captured at a designated downstream site and releasing marked smolts back into the population at an upstream site. Marked smolts subsequently recovered at the downstream site are counted to estimate capture probability (trap efficiency), which is used to estimate smolt abundance for a segment of the population. This procedure is temporally stratified such that each trap efficiency trial is discretely paired with one capture period; this can typically be accomplished by releasing marked smolts at relatively short intervals (a few days) with little chance of recaptured fish occurring in later strata. This approach accounts for potential temporal changes in capture probability under a fairly modest assumption of stratum consistency. The method simplifies the generalized 2-sample stratified design and provides some important advantages: (1) because marking occurs in discrete intervals, personnel costs are substantially reduced; (2) because each release of marked smolts corresponds to one capture period, only one type of mark is needed, which greatly simplifies marking procedures and recapture tallying; and (3) when only one capture site is used, material costs are reduced by about half. We present approximately unbiased abundance and variance estimators of the total smolt population and develop a method of estimating the number of smolts to be marked. A parametric bootstrap technique for quantifying precision is also developed. An example of the method is given using the 1997 sockeye salmon Oncorhynchus nerka smolts migrating from Akalura Lake, Kodiak Island, Alaska. The Akalura Lake study included a weir count of smolts, which we used to evaluate the accuracy of the M-R estimate.

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Deep-Water Bark Accumulation and Benthos Richness at Log Transfer and Storage Facilities

Ben Kirkpatrick, Thomas C. Shirley, and Charles E. O'Clair - Vol. 5(2):103-115. 1998.

A small, manned submersible was used to determine the extent of bark accumulation and its effects on the epifaunal macrobenthos at depths from 20-130 m at log transfer facilities (LTFs) and log rafting facilities (LRFs) in Dora Bay, Prince of Wales Island, Alaska. Continuous videotaping from an external fixed camera was conducted along 6 transects located near LTFs and LRFs and along 3 transects in a similar, adjacent area not used as an LTF or LRF. Bark and woody debris accumulations and kinds and numbers of organisms were recorded by depth for 3 general habitat types (steep, rocky; moderate incline, cobble; flat, silty) with and without bark. Bark accumulation was found to 40-m depth on 6 dives, and to 70-m depth on 3 dives. Of 91 taxa observed during the study, most (69 species) were found on rocky, bark-free habitat; significantly reduced species richness was found in all bark-dominated habitats. Bark and debris from LTFs appeared to be displaced down slope into adjacent, deeper areas; this is the first published account of bark and woody debris accumulation below 20-m depth. In suitable habitats, manned submersibles or remotely operated vehicles appear to be useful tools for monitoring bark accumulation and investigating the effects of logging facilities.

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Stock-Recruitment Relationship for Bristol Bay Tanner Crab

Jie Zheng and Gordon H. Kruse - Vol. 5(2):116-130. 1998.

We developed a method to estimate male reproductive potential and effective spawning biomass and used the results from a length-based model to develop a stock-recruitment relationship for Bristol Bay Tanner crab Chionoecetes bairdi. Weak and strong recruitment occurred with both low and high effective spawning biomass; however, recruits are not strongly associated with effective spawning biomass. Recruitment is highly autocorrelated. The strongest recruitment is almost 100 times as large as the weakest recruitment, and the largest effective spawning biomass is more than 10 times as large as the lowest. An autocorrelated Ricker curve is flatter and fits the observations better than an ordinary Ricker curve. Much of the recruitment variation can be explained by autocorrelation or cycle; thus, environmental factors are likely to play a very important role in recruitment success.

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Spring and Summer Whole-Body Energy Content of Alaskan Juvenile Pacific Herring

A. J. Paul and J. M. Paul - Vol. 5(2):131-136. 1998.

During the spring and summer of 1996 and 1997, we examined the whole-body energy content (WBEC) of Pacific herring Clupea pallasi less than or equal than 165 mm standard length (SL) from Prince William Sound, Alaska. From May to October, somatic energy (kJ·g-1 wet weight) exhibited a wide range of values relative to length. Young-of-year recruits, which appeared in July of both years, typically had WBEC of 2-3 kJ·g-1 wet weight after metamorphosis, and older fish had WBEC of 4-6 kJ·g-1 wet weight. By October the WBEC of juvenile herring was typically 4-6 kJ·g-1 wet weight. The consequences of the large seasonal and size-related variability in WBEC in juvenile herring are discussed relative to the transfer of energy to predators.

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An Egg-Loss Correction for Estimating Spawning Biomass of Pacific Herring in Prince William Sound, Alaska

Christopher N. Rooper, Lewis J. Haldorson, and Terrance J. Quinn II - Vol. 5(2):137-142. 1998.

Spawning biomass of Pacific herring Clupea pallasi populations is commonly estimated from surveys that quantify their egg deposition. Because surveys occur after spawning, a correction for egg loss is required. We estimated this correction factor for the 1995 herring stock in Prince William Sound, Alaska, using an egg-loss model. The model was based on the cumulative time of exposure to air during egg incubation. The correction factor for the percentage of eggs lost between spawning and spawn-deposition surveys was estimated at 31% (SE = 2.2%). This value is much higher than the value previously assumed for Alaska stocks. Because interannual variability in the egg-loss correction may occur, we suggest that future spawn surveys be accompanied by egg-loss studies.

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Age and Marine Survival of Ocean-Type Chinook Salmon Oncorhynchus tshawytscha from the Situk River, Alaska

John F. Thedinga, Scott W. Johnson, and K V. Koski - Vol. 5(2):143-148. 1998.

Chinook salmon Oncorhynchus tshawytscha smolts were sampled for scales, coded-wire-tagged, and released in the Situk River, Alaska. As returning adults, they were then sampled for scales to compare freshwater age composition at release and recovery and to estimate marine survival. Of 10,191 chinook salmon smolts tagged (July 1989), 98% were age 0. From 1991 through 1993, 23 of 35 tagged chinook salmon adults recovered in the commercial fishery and spawning-ground surveys had readable scales that identified 87% of the fish as age 0. (ocean-type). Estimated marine survival was 2.9%, excluding returning age-0.1 jacks. We concluded that ocean-type chinook salmon are the predominate life history type for the Situk River. Situk River chinook salmon are unique because they are the only known stock in Alaska that migrates to sea primarily at age 0.

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